Various substituted amidothionophosphorus compounds are known to be useful as insecticides and acaricides. Typical insecticidal properties of such compounds are taught in Belgian Patent No. 724,68l. In particular, it is known from U.S. Pat. No. 3,922,324, that certain O-aryl-thionoalkanephosphonic acid ester-formamidines or imino-ethers, in which the aryl group is an optionally halogen-substituted phenyl group, have pesticidal activity.